The invention relates to a knife carriage as is utilized in face-to-face weaving machines.
On a face-to-face weaving machine two backing fabrics are woven one above the other whereby two weft threads are simultaneously inserted in two sheds located one above the other. These backing fabrics are connected by pile warp threads. On the machine these pile warp threads are cut through with a cutting device so that ultimately a top and a bottom fabric are obtained. The cutting device of a face-to-face weaving machine consists of a cutting bench, a so-called knife carriage or cutting carriage, and a drive for the movement of the knife or cutting carriage.
The cutting bench has a guiding with e.g. a trapezoid-shaped cross-section (dovetail) on which the knife carriage is moved back and forth. On the knife carriage a cutting knife is attached with which the fabric is separated into bottom and top fabric. The knife carriage is pulled back and forth on the guideway by a cord that is for example alternately wound up and unwound on a drive cylinder. For this purpose a drive device is for example utilized as described in the European patent publication EP 0 399 501.
In order to obtain a perfect cut the knife carriage may not wobble during its movement on the cutting bench and nevertheless a certain play needs to be present in order for it to be able to slide. For that purpose the supporting plate will be as stiff as possible in order to keep the sliding surfaces flat. The sliding surfaces themselves are subject to wear and tear and need therefore to be easily replaceable. For this purpose detachable sliding parts have been developed. In order for accurate adjustment of the guiding path also to be possible at least two sliding parts will be adjustable. Considering the knife carriage is subject to a fast back and forth movement, the knife carriage will also be made as light as possible in order to limit the tractive forces in the cord and in order not to load the drive mechanism unnecessarily by providing a higher power in the drive.
Such cutting devices are for example known from the German patent publication DE OS 31 18 188. The knife carriage described therein has interchangeable and adjustable sliding parts. In order to limit the mass of the knife carriage the supporting plate is made of light metal and the sliding parts of synthetic material provided with a hard bearing material. In the supporting plate of the knife carriage two slots are made for receiving the sliding parts. Through the milling of these slots a light metal plate has a tendency to buckle. The supporting plate is however made of a solid piece and extends in width over the entire width of the trapezoid-shaped guiding surface plus the width of the oblique side sliding surfaces. The place where the sliding parts are screwed on requires extra mass which makes the carriage wider and therefore makes it weight more. Such a knife carriage weighs around 450 g. For the present operating speeds of a velvet weaving machine around 400 revs./min at 1.50 m weaving width and 150 revs./min for a 4.00 m wide face-to-face carpet weaving machine this mass of a knife carriage is still too heavy: the driving cord breaks prematurely and the drive consumes a large amount of power.
DE GM 87 10 823 describes a knife carriage also with interchangeable and adjustable sliding surfaces. In order to limit the mass here the supporting plate is made of synthetic material. With this embodiment there are two openings in the longitudinal direction of the supporting plate, through which the supporting plate loses rigidity and the plate has the tendency to buckle. In those openings there comes a type of reinforcement in order to give the supporting plate more tensile strength and in order to increase the rigidity in longitudinal direction. This adaptation is reflected in the cost price. For the positioning of the sliding surfaces four millings are necessary. This is not conducive to the sliding surfaces being flat. The sliding surfaces have extra mass at the locations where the attachment screws come and the supporting plate is because of this also wider than the underlying guiding surface. Such a knife carriage ultimately still weighs 400 g. The attachment of the cord with clamps and two bolts causes a bending moment in the supporting plate so that this will deform through which the knife carriage will wobble during its back and forth movement.
In DE PS 36 14 992 a knife carriage is described with built-in dry lubricant. The sliding surfaces have extra mass at the oblique sides of the trapezoid-shaped guide on the cutting bench. Through the one-sided attachment the sliding surfaces buckle and there is more wear and tear and therefore premature play with increased chance of bad cutting.
This is also the case with a knife carriage described in DE GM 86 27 022.
In DE OS 30 06 497 a knife carriage is described with roller wheels as guiding means. With such an embodiment an extra wide supporting plate is necessary, which gives an unacceptably heavy knife carriage.